JPH0717213A - Pneumatic radial tier for heavy load - Google Patents

Abstract

PURPOSE:To provide a heavy load pneumatic radial tire which can prevent effectively the occurrence of partial wear at each shoulder end portion without causing inconvenience such as a cracking. CONSTITUTION:In the case of a heavy load pneumatic radial tire having the tread pattern of a rib basis at its tread portion 1, a plurality of sipes 8 are provided at each buttress portion 2 connected to the side edge of the tread portion 1, and these sipes 8 are inclined in regard to a tire diametric direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty pneumatic radial tire having a rib-based pattern on a tread, and more specifically, it is effective in causing uneven wear at shoulder end portions without causing problems such as cracks. The present invention relates to a heavy-duty pneumatic radial tire capable of being prevented.

[0002]

2. Description of the Related Art Pneumatic radial tires having a rib-based pattern used for heavy loads such as trucks and buses tend to widen the tread deployment width in order to improve uneven wear resistance. When the spread width is widened, there is a drawback that shoulder wear tends to occur at the shoulder end portion, especially on the steering shaft side. That is, shoulder drop wear is caused by the fact that the ground contact pressure at the shoulder end becomes high when a load is applied, cornering force is applied in this state, and the shoulder end having a small diameter with respect to the center part having a large diameter rotates when the tire rotates. It is caused by being dragged by the diameter difference. Therefore, widening the tread expansion width as described above increases the concentration of the ground contact pressure at the shoulder end portion, and further increases the diameter difference between the center portion and the shoulder end portion, which promotes shoulder drop wear. .

As a countermeasure, the shoulder end of the tread is rounded to form a round shoulder, or a plurality of sipes extending in the tire radial direction and narrow grooves extending in the tire circumferential direction are provided at the shoulder end to improve the rigidity of this portion. It has been proposed to prevent uneven wear as described above by lowering the ground pressure so that it does not concentrate on the shoulder end.

However, in the case of the round shoulder, the shoulder drop wear due to the differential drag is promoted, and when a plurality of sipes are provided at the shoulder end, heel and toe wear is caused, and the shoulder end is also worn. When the narrow groove is provided in the groove, a crack may be generated in the groove bottom due to stone trapping in the narrow groove, and the thin rib outside the narrow groove may be damaged. In this way, to provide round shoulders, sipes or narrow grooves that appear on the tread surface side at the shoulder end,
Although effective in terms of rigidity reduction, they all had some problems.

Therefore, by providing a plurality of sipes extending in the tire radial direction and narrow grooves extending in the tire circumferential direction as described above in the buttress portion connected to the side edge of the tread, the rigidity of the shoulder end portion is reduced, There has been proposed a device which avoids the above inconvenience. However, when sipe or narrow groove is provided in the buttress,
Although it is possible to satisfy some performance,
For example, it was not always sufficient when traveling on a road with many curves or when traveling under a high load. That is, if the space between the sipes provided in the buttress portion is made close, the number of sipes increases, and thus edge cracks are likely to occur on the surface. Becomes higher and uneven wear is more likely to occur, and if the sipes are formed thicker in a state where the intervals between sipes are sparse, the rigidity in the tire circumferential direction becomes uneven and wavy wear is likely to occur. On the other hand, if the narrow groove provided in the buttress portion is wide and deep, a fatal crack that reaches the belt layer at the groove bottom may occur due to the deformation of the buttress portion, and conversely if the narrow groove is made narrow and shallow. Although it is possible to prevent the occurrence of cracks in the groove bottom, uneven wear is likely to occur due to insufficient rigidity reduction.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy-duty pneumatic radial tire capable of effectively preventing occurrence of uneven wear at the shoulder end without causing inconvenience such as cracking. To provide.

[0007]

Means for Solving the Problems A heavy duty pneumatic radial tire of the present invention for achieving the above object is a heavy duty pneumatic radial tire having a rib-based tread pattern on a tread, wherein a side edge of the tread is provided. A plurality of sipes are provided in the continuous buttress portion, and the plurality of sipes are inclined with respect to the tire radial direction.

Since the buttress portion is provided with the plurality of sipes inclined with respect to the tire radial direction, the buttress portion is flexibly deformed like a pantograph.
Stress is less likely to concentrate on the sipe edge, and even if the number of sipes is small and the width is narrow, it is possible to uniformly cover a wide area in the tire circumferential direction and effectively reduce the rigidity.
Therefore, in a heavy-duty pneumatic radial tire having a rib-based pattern, even when a plurality of sipes are provided in the buttress portion so as to effectively prevent the occurrence of uneven wear at the shoulder end, the occurrence of sipe edge cracks Can be prevented. Further, as described above, the sipe provided in the buttress portion does not cause a fatal crack reaching the belt layer at the groove bottom like a narrow groove extending in the tire circumferential direction.

The structure of the present invention will be described below in detail with reference to the accompanying drawings. 1 to 4 show a pneumatic radial tire for heavy load according to an embodiment of the present invention. In the figure, 1 is a tread portion, 2 is a buttress portion which is continuous with a side edge of the tread 1, 3 is a carcass layer mounted between a pair of left and right bead portions, and 4 is arranged outside the carcass layer 3 in the tread portion 1. It is a belt layer. The carcass layer 3 is composed of at least one layer in which reinforcing cords form substantially 90 ° with respect to the tire circumferential direction, and as the reinforcing cords, metal cords such as steel or organic fiber cords such as nylon, polyester, polyaramid or the like are used. Preferably used. The belt layer 4 is composed of at least two layers made of a metal cord such as steel, and is designed to enhance the rigidity of the tread portion 1. More preferably, the belt layer 4 is composed of at least two tensile strength layers and one reinforcing layer, and the reinforcing cords of the tensile strength layer form 15 ° to 30 ° with respect to the tire circumferential direction, and There is a relationship in which adjacent layers intersect with each other with the tire circumferential direction sandwiched therebetween, and the reinforcing cords of the reinforcing layer form 40 ° to 75 ° with respect to the tire circumferential direction. Good.

The tread portion 1 is provided with a plurality of zigzag-shaped main grooves 5 extending in the tire circumferential direction. The main grooves 5 form a plurality of ribs 6 on the center side of the tread. The shoulder ribs 7 are separately formed on each of the above. On the other hand, in the buttress section 2,
A plurality of sipes 8 inclined with respect to the tire radial direction are provided at intervals over the entire circumference of the tire. Adjacent sipes 8 and 8 are partially overlapped with each other in the tire radial direction.

When a plurality of sipes 8 inclined with respect to the tire radial direction are provided on the buttress portion 2 connected to the side edge of the tread portion 1 as described above, the presence of these sipes 8 makes the buttress portion 2 look like a pantograph. Since the rigidity of the shoulder end portion is effectively reduced due to the deformation, the ground contact pressure is less likely to concentrate on this portion. Therefore, in heavy-duty pneumatic radial tires having a rib-based pattern, the shoulder rib 7 can be effectively worn down. Can be prevented. Further, in the sipe 8 inclined in the tire radial direction, stress is less likely to be concentrated on the edges of the surface thereof, and even if the number is small and the width is narrow, a wide area in the tire circumferential direction can be covered and the number of edges can be reduced. Therefore, it is possible to prevent the occurrence of sipe edge cracks as compared with the case where a large number of sipes are provided in parallel with the radial direction as in the conventional case.

In the present invention, the inclination angle θ of the sipe 8 with respect to the tire radial direction is preferably 15 ° to 45 °. By setting the inclination angle θ of the sipe 8 as described above, the above pantograph effect can be obtained. Further, it is preferable that the adjacent sipes 8 and 8 are arranged so that parts thereof overlap each other in the tire radial direction. By forming the lap portion in this manner, it is possible to more effectively reduce the rigidity, and it is possible to make the rigidity uniform in the tire circumferential direction.

Regarding the sipe 8, the distance S from the tread surface is preferably 110 to 300% of the depth G of the main groove 5, and the length L in the tire radial direction is 5 of the depth G of the main groove 5.
The depth D is preferably 0 to 200%, and the depth D is preferably 20 to 100% of the depth G of the main groove 5. Also,
The pitch interval P is preferably 5 to 25% of the tread development width TW, the length W in the tire circumferential direction is preferably 8 to 25% of the tread development width TW, and the sipe width T
Is preferably 0.8 to 6 mm. The formation position or the size of the sipe 8 is out of the above range, and the buttress portion 2
If the rigidity of is too high, the contact pressure at the shoulder end will not be sufficiently reduced and uneven wear will occur easily.
Conversely, if the rigidity of the buttress portion 2 is too low, sipe edge cracks are likely to occur.

The sipe 8 is not limited to the linear shape in plan view as in the above embodiment, but can be various shapes as shown in FIGS. When both end portions 8a of the sipe 8 are rounded as shown in FIG. 5 or both end portions 8b of the sipe 8 are bent as shown in FIG. 6, stress concentration on the edges is relaxed, so that sipe edge cracks Occurrence can be prevented more effectively. In addition, as shown in FIG. 7, the inclination direction of the sipe 8 may be different from each other.
As described above, the sipe 8 may be bent at the center and both sides 8c thereof may be inclined with respect to the tire radial direction.

[0015]

EXAMPLE A heavy-duty pneumatic radial tire having a tire size of 11R22.5 14PR and having rib patterns as shown in FIGS. 2 and 3, the conventional tires 1 to 1 having different buttress portions processed as described below. Four
And the tires of the present invention were manufactured. In each tire, the tread development width TW was 220 mm and the main groove depth G was 15 mm. The distance S from the tread surface of the sipe provided in the buttress portion was 25 mm, the length L in the tire radial direction was 15 mm, and the depth D was 7 mm. Conventionally, the tire 1 buttress portion was not processed at all. Conventional tire 2 A plurality of sipes extending substantially parallel to the tire radial direction (FIG. 9) are provided in the buttress portion of the conventional tire 2 over the entire circumference of the tire, the pitch interval P between these sipes is 8 mm, and the sipes width T is 2
mm. A plurality of sipes (FIG. 10) extending substantially parallel to the tire radial direction are provided in the conventional tire 3 buttress portion over the entire circumference of the tire, and a pitch interval P between these sipes is set to 24 mm and a sipes width T is set.
Was set to 2 mm. A plurality of sipes (FIG. 11) extending substantially parallel to the tire radial direction are provided in the conventional tire 4 buttress portion over the entire circumference of the tire, and the pitch interval P between these sipes is set to 24 mm and the sipes width T is set.
Was set to 8 mm. A plurality of sipes (FIG. 4) inclined with respect to the tire radial direction are provided in the tire 1 buttress portion of the present invention over the entire circumference of the tire, the inclination angle θ of these sipes is 20 °, and the pitch interval P is 24 mm.
And the sipe width T is 8 mm and the tire circumferential length W is
Was 32 mm.

Assembling these conventional tires 1 to 4 and the tire of the present invention into a wheel having a rim size of 22.5 × 8.25,
Each was mounted on the front shaft and drive shaft of a large-sized vehicle (2-D4), the air pressure was 7.0 kg / cm ² , and after traveling 20,000 km on a paved road, the uneven wear and the occurrence of cracks at the sipe edge were observed, The results are shown in Table 1.

The uneven wear was observed in the tire of the front shaft, and those that hardly occurred were indicated by ◯, those that occurred a little were indicated by Δ, and those that occurred significantly were indicated by X. Further, cracks were observed in the tire of the drive shaft, and those that were scarcely generated were indicated by ◯, those that were slightly generated were indicated by Δ, and those that were significantly generated and were not practical are indicated by ×.

[0018] As can be seen from Table 1, the tire of the present invention was able to effectively prevent the occurrence of uneven wear without causing sipe edge cracks. On the other hand, the conventional tire 1
Caused significant shoulder drop wear, and the conventional tire 2 provided with a large number of sipes did not cause uneven wear, but had significant sipe edge cracks. Further, the conventional tires 3 and 4 having a reduced number of sipes hardly generated sipe edge cracks, but the conventional tire 3 suffered shoulder drop wear and the conventional tire 4 suffered corrugated wear.

[0019]

As described above, according to the present invention, in a heavy-duty pneumatic radial tire having a rib-based tread pattern on a tread, a plurality of sipes are provided in a buttress portion connected to a side edge of the tread, By inclining multiple sipes with respect to the tire radial direction,
Since the buttress portion flexibly deforms like a pantograph, stress is less likely to concentrate on the sipe edge, and even if the number of sipes is small and the width is narrow, it uniformly covers a wide area in the tire circumferential direction, effectively reducing rigidity. It will be possible to do. Therefore, it is possible to effectively prevent occurrence of uneven wear at the shoulder end portion without causing inconvenience such as cracking.

[Brief description of drawings]

FIG. 1 is a perspective sectional view showing a main part of a heavy duty pneumatic radial tire according to an embodiment of the present invention.

FIG. 2 is a development view showing a tread pattern of a heavy duty pneumatic radial tire according to an embodiment of the present invention.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is an enlarged plan view showing the sipe in FIG.

FIG. 5 is a plan view showing a modified example of the sipe according to the present invention.

FIG. 6 is a plan view showing a modified example of the sipe according to the present invention.

FIG. 7 is a plan view showing a modified example of the sipe according to the present invention.

FIG. 8 is a plan view showing a modified example of the sipe according to the present invention.

FIG. 9 is a plan view showing a sipe provided in a buttress portion of a conventional heavy-duty pneumatic radial tire.

FIG. 10 is a plan view showing sipes provided in a buttress portion of a conventional heavy-duty pneumatic radial tire.

FIG. 11 is a plan view showing a sipe provided in a buttress portion of a conventional heavy-duty pneumatic radial tire.

[Explanation of symbols]

 1 Tread part 2 Buttress part 7 Shoulder rib 8 Sipe

Claims (1)

[Claims] 1. A heavy-duty pneumatic radial tire having a rib-based tread pattern on a tread, wherein a plurality of sipes are provided in a buttress portion connected to a side edge of the tread, and the plurality of sipes are inclined with respect to a tire radial direction. Pneumatic radial tire for heavy loads.